Metatag description from 1st post in phpbb (old version 2006)

General information for the website: Its an old phpbbforum
Kind of development: Customization of existing website
Description of every page/module: A description metatag on every page of my forum.
- on the index static
- on viewforum based on the category description
- on viewtopic dynamic, get the first post, get rid of bbcodes en Shorten description if it's longer than 150 characters.
Description of requirements/features: I ve found a simular modification for a phpbb 3.0 forum. I think a great part of that code can be used to get the job done in the old version. https://www.phpbb.com/community/viewtopic.php?f=46&t=2122998
I dont need the metatag keyword metatag. This is my forum: http://www.klusidee.nl/Forum.
Extra notes: I think the files you need to add code is:
index.php
viewforum.php
viewtopic.php
pageheader.php

de templatefile overallheader.php